Antarctic ice melting from below - World Environment Day 5 June

This article originally part of NASA research is published here as World Environment Day is on 5 June 2012 and this information can be used by activists. Video accompanying this story will be published later here.

Warm ocean currents attacking the underside of ice shelves
are the dominant cause of recent ice loss from Antarctica, a new study
using measurements from NASA's Ice, Cloud, and land Elevation Satellite
(ICESat) revealed.

How was this information discovered ?
An international team of scientists used a combination of satellite
measurements and models to differentiate between the two known causes of
melting ice shelves: warm ocean currents thawing the underbelly of the
floating extensions of ice sheets and warm air melting them from above.
The finding, published today in the journal Nature, brings scientists a
step closer to providing reliable projections of future sea level rise.

What did the researchers Conclude ?
The researchers concluded that 20 of the 54 ice shelves studied are
being melted by warm ocean currents. Most of these are in West
Antarctica, where inland glaciers flowing down to the coast and feeding
into these thinning ice shelves have accelerated, draining more ice into
the sea and contributing to sea-level rise. This ocean-driven thinning
is responsible for the most widespread and rapid ice losses in West
Antarctica, and for the majority of Antarctic ice sheet loss during the
study period.

"We can lose an awful lot of ice to the sea without ever having summers
warm enough to make the snow on top of the glaciers melt," said the
study's lead author Hamish Pritchard of the British Antarctic Survey in
Cambridge, United Kingdom. "The oceans can do all the work from below."

What was the methodology used ?
To map the changing thickness of almost all the floating ice shelves
around Antarctica, the team used a time series of 4.5 million surface
height measurements taken by a laser instrument mounted on ICESat from
October 2003 to October 2008. They measured how the ice shelf height
changed over time and ran computer models to discard changes in ice
thickness because of natural snow accumulation and compaction. The
researchers also used a tide model that eliminated height changes caused
by tides raising and lowering the ice shelves.

"This study demonstrates the power of space-based, laser altimetry for
understanding Earth processes," said Tom Wagner, cryosphere program
scientist at NASA Headquarters in Washington." Coupled with NASA's
portfolio of other ice sheet research using data from our GRACE mission,
satellite radars and aircraft, we get a comprehensive view of ice sheet
change that improves estimates of sea level rise."

Why this discovery was possible now ? Why not years ago ?
Previous studies used satellite radar data to measure the evolution of
ice shelves and glaciers, but laser measurements are more precise in
detecting changes in ice shelf thickness through time. This is
especially true in coastal areas. Steeper slopes at the grounding line,
where floating ice shelves connect with the landmass, cause problems for
lower-resolution radar altimeters.

Tell in brief about the satellites used ?
ICESat was the first satellite specifically designed to use laser
altimetry to study the Earth's polar regions. It operated from 2003 to
2009. Its successor, ICESat-2, is scheduled for launch in 2016.

What does this study Demonstrate ?
According to Jay Zwally, ICESat project scientist at NASA's Goddard
Space Flight Center in Greenbelt, Md. "study demonstrates the urgent need for ICESat-2 to get into
space," He further says "We have limited information on
the changes in polar regions caused by climate change. Nothing can look
at these changes like satellite measurements do."

What else this new research observe ?
The new research also links the observed increase in melting that occurs
on the underside of a glacier or ice shelf, called basal melt, and
glacier acceleration with changes in wind patterns.

"Studies have shown Antarctic winds have changed because of changes in
climate," Pritchard said. "This has affected the strength and direction
of ocean currents. As a result warm water is funnelled beneath the
floating ice. These studies and our new results suggest Antarctica's
glaciers are responding rapidly to a changing climate."

What about ice on shelf surfaces ? Role of Winds ?
A different picture is seen on the Antarctic Peninsula, the long stretch
of land pointing towards South America. The study found thinning of the
largest ice shelf on the peninsula can be explained by warm summer
winds directly melting the snow on the ice shelf surfaces. The patterns
of widespread ocean-driven melting and summer melting on the Antarctic
Peninsula can be attributed to changing wind patterns.

The study was carried out by an international team from the British
Antarctic Survey, Utrecht University in Utrecht, Netherlands, the
University of California in San Diego and the non-profit research
institute Earth and Space Research in Corvallis, Ore.

What is ICESat and ICESat-2 ?
ICESat (Ice, Cloud,and land Elevation Satellite) is the benchmark Earth Observing System mission for measuring ice sheet mass balance, cloud and aerosol heights, as well as land topography and vegetation characteristics. From 2003 to 2009, the ICESat mission provided multi-year elevation data needed to determine ice sheet mass balance as well as cloud property information, especially for stratospheric clouds common over polar areas. It also provided topography and vegetation data around the globe, in addition to the polar-specific coverage over the Greenland and Antarctic ice sheets.

ICESat-2 : The Ice, Cloud,and land Elevation Satellite-2 (ICESat-2) is the 2nd-generation of the laser altimeter ICESat mission (January 13, 2003 to August 14, 2010). ICESat-2 is scheduled for launch in early 2016.

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